Magnetoresistive sensors can include giant magnetoresistive (GMR), tunnel magnetoresistive (TMR), anisotropic magnetoresistive (AMR) and other technologies, referred to collectively as xMR technologies. For some applications of these xMR sensors, very high shape anisotropy of the xMR strip, i.e., a length of the xMR strip being much greater than the width or vice-versa, is needed. For example, a multi-turn sensor for sensing a number of turns of a rotating magnetic field needs a very narrow xMR strip width, such as on the order of 200 nanometers (nm) or less. The width also must be very accurate and uniform across a wafer and from wafer to wafer to achieve a high manufacturing yield. Further, no significant chemical modification of the etched side walls after processing can occur, as such corrosion can cause a performance drift.
In other words, the manufacturing challenges for xMR sensors needing very high shape anisotropy are many. Conventional etch processes suitable for mass production of xMR stacks make meeting these challenges very difficult. For example, ion beam milling processes are often used in conventional manufacturing processes. Chemical etches or resist removal processes used therein, however, can damage sidewalls, thereby degrading magnetic performance, and can provide non-uniform behaviors over the wafer, both significant drawbacks. Ion beam milling processes are also slow and typically not suitable for mass production. Therefore, a need remains for an improved xMR sensor.